Patent document 1: JP 2000-73635 A (U.S. Pat. No. 6,552,649 B)
A keyless entry system or smart entry system is conventionally known to lock and unlock a door of a vehicle without need of a user inserting a key into a key cylinder.
In the keyless entry system, a user manipulates a button in a key of a portable terminal to thereby transmit a wireless signal; upon receiving the wireless signal, an in-vehicle apparatus locks or unlocks a door of the vehicle.
In contrast, in the smart entry system, an in-vehicle apparatus (smart ECU) mounted in a vehicle transmits a request signal; a smart key (portable terminal) transmits a response signal in response to the request signal. The in-vehicle apparatus collates the received response signal and unlocks and locks a door of the vehicle based on the collation result.
Patent document 1 proposes a vehicular control system that transmits an electric wave of high frequency from an in-vehicle apparatus in order to extend a detection area of a portable transceiver in an area surrounding a vehicle.
Further, Patent document 1 proposes a configuration which has short-range areas and long-range areas larger than the short-range areas in an area surrounding a vehicle. Further, according to a degree of an approach of the portable transceiver towards the vehicle, the short-range areas and the long-range areas are switched therebetween, thereby detecting the approach of the portable transceiver. The short-range area is a reachable region of a short-range use signal carried on electric waves of low frequency. The long-range area is a reachable region of a long-range use signal carried on electric waves of high frequency.
When entering the long-range area where the electric waves of high frequency are transmitted, the portable transceiver replies a reply signal. The in-vehicle apparatus recognizes the reply signal, thereby detecting the portable transceiver. Thus, unnecessary consumption of an in-vehicle battery is prevented because the in-vehicle apparatus switches the detection areas of the portable transceiver.